JP6496080B2 - Piezoelectric sensor - Google Patents

Description

  The present invention relates to a piezoelectric sensor that measures a physical quantity with a piezoelectric element, integrates a current signal of a measurement result, amplifies it, and outputs it.

  Piezoelectric sensors that use piezoelectric elements that generate charges according to the amount of physical deformation are often used as sensors for measuring engine combustion pressure because they have excellent sensitivity and do not lose accuracy even in high-temperature environments. .

  FIG. 3 is a diagram illustrating an example of a configuration of a conventional piezoelectric sensor. In FIG. 3, 301 is a piezoelectric element, 302 is a DC blocking capacity, 303 is a discharge resistance, 304 is a charging capacity, 305 is an operational amplifier for integration, 312 is a feedback terminal, 313 is a signal output terminal, 315 Denotes a signal input terminal, 306 denotes a reference voltage source, 307 denotes an amplification resistor a, 308 denotes an amplification resistor b, 309 denotes an operational amplifier for amplification, and 310 denotes an integrated circuit.

  The piezoelectric element 301 has a pair of electrodes on its surface, and outputs a charge signal from the electrodes according to the stress applied to the piezoelectric element 301. In the piezoelectric element 301, the configuration in which the wiring is routed from the electrode and input to the circuit block becomes very complicated. Therefore, as shown in FIG. 3, one of the electrodes is grounded and a signal is taken from the other electrode. Commonly used. The other electrode is connected to the negative input terminal of the integrating operational amplifier 305 via a DC blocking capacitor 302.

  The integration operational amplifier 305 has a charge capacitor 304 and a discharge resistor 303 connected in parallel between the negative input terminal and the output terminal, and a reference voltage source 306 connected to the positive input terminal. An integration circuit is configured by 305, the charge capacitor 304, and the discharge resistor 303.

  The AC charge signal output from the piezoelectric element 301 is accumulated in a charging capacitor 304 provided between the input and output of the integration operational amplifier 305 via a DC blocking capacitor 302 for cutting a DC component, and is integrated. It is converted into the signal Vo1. Here, by using the integration operational amplifier 305 having a high input impedance, it is possible to accurately detect even when the charge signal of the piezoelectric element 301 is very small. The discharge resistor 303 is provided to prevent the charge capacitor 304 from being saturated when the positive / negative balance of the AC charge signal is not uniform. The charge / discharge time constant determined by the charge capacitor 304 and the discharge resistor 303 is The period of the detection signal needs to be sufficiently long.

  The reference voltage source 306 is for applying a predetermined bias voltage to the integrating circuit and the amplifier circuit, and a voltage regulator circuit using a band gap voltage of a transistor is generally used.

  An amplifier circuit that amplifies the output signal Vo1 of the integration operational amplifier 305 and outputs an output signal Vout as a piezoelectric sensor is provided at the subsequent stage of the integration operational amplifier 305. The amplification circuit is configured by an amplification operational amplifier 309, an amplification resistor a307, and an amplification resistor b308. The amplification resistor b308 is connected between the negative input terminal and the output terminal of the amplification operational amplifier 309, and the positive input terminal. In this configuration, a reference voltage source 306 is connected via an amplification resistor a307.

  The circuit block can be composed of discrete components, but it is advantageous to build it into a single integrated circuit in terms of space and cost. In the conventional example shown in FIG. 3, an integration operational amplifier 305, an amplification operational amplifier 309, a reference voltage source 306, an amplification resistor a307, and an amplification resistor b308 are integrated to form an integrated circuit 310. Even when the circuit block is formed as a single integrated circuit, the charge capacitor 304 and the discharge resistor 303 are generally provided outside the integrated circuit 310. This is because the charging capacity 304 and the discharge resistance 303 are usually large, so that it is difficult to make them inside the integrated circuit 310. An input / output terminal is provided at a connection point between the integrated circuit 310 and the outside. A connection point between the integration operational amplifier 305 and the piezoelectric element 301 is a signal input terminal 315, an output of the integration operational amplifier 305, a discharge resistor 303, and a charge. A connection point with the capacitor 304 is provided with a feedback terminal 312, and a connection point between the output of the operational amplifier for amplification 309 and the outside is provided with a signal output terminal 313.

  FIG. 5 is a diagram showing another example of a conventional piezoelectric sensor. The piezoelectric sensor includes an integration circuit including a piezoelectric element 501, an integration operational amplifier 505, a discharge resistor 503, and a charge capacity 504, a reference voltage source 506, and an amplification operational amplifier 509. In the conventional example shown in FIG. 3, the charge capacitor 304 and the discharge resistor 303 are provided between the input and output of the integration operational amplifier 305. However, in the piezoelectric sensor shown in FIG. In this configuration, a charge capacity 504 and a discharge resistor 503 are provided between the terminal and the reference voltage source 506. In FIG. 3, the amplifier circuit is a one-stage forward rotation amplifier circuit. In this example, the output signal of the integration operational amplifier 505 is input to the negative input terminal of the amplification operational amplifier 509 via the amplification resistor a507. In addition, an amplification resistor b508 is connected between the negative side input terminal and the output terminal, and the positive side input terminal is configured by a one-stage inverting amplifier circuit connected to the reference voltage source 506. The amplifier circuit can also have a multi-stage configuration.

JP 2009-115484 A

  The variation in the measurement sensitivity of the output signal Vout of the piezoelectric sensor for each product needs to be minimized. However, the magnitude of the charge signal generated from the piezoelectric element has a relatively large difference in the generated charge due to slight differences in the generation process of the piezoelectric element crystal and processing accuracy, and is required for the output signal Vout of the piezoelectric sensor. It is difficult to meet accuracy.

  For this reason, it is a common practice to provide a gain adjusting mechanism in the amplifier circuit and adjust the gain in the sensor assembly process to ensure the accuracy of the output signal Vout.

  FIG. 4 is an example of a ladder resistor for adjusting the amplification factor, and is composed of a four-stage resistor circuit (R1 to R4) connected in series with the resistor Rf. By cutting the wiring from P1 to P4 of the resistance circuit at each stage, 16 resistance values can be set from the minimum Rf to the maximum Rf + R1 + R2 + R3 + R4. By using the ladder resistor as the amplification resistor a, the amplification resistor b, or both, and cutting the wirings P1 to P4 with a laser or an end mill, the amplification factor can be adjusted.

  There is also a method in which a commercially available laser trimmable resistor is used for the amplification resistor a, the amplification resistor b, or both, and the resistance value is adjusted with a laser.

  However, these adjustment methods have a problem that the amplification factor cannot be adjusted when the sensor is completed. FIG. 6 is an exploded perspective view showing the structure of a combustion pressure sensor which is an example of a piezoelectric sensor. A diaphragm head 601 for transmitting the combustion pressure to the piezoelectric element 604 is provided at the front end portion of the front housing 603, and a fixing screw 602 for fixing the combustion pressure sensor to the engine is provided in the middle. . The piezoelectric element 604, the conductive wire 605, the circuit board 606, and the circuit case 607 are housed in a front housing 603 and a rear housing 609, and the front housing 603 and the rear housing 609 are welded to constitute a combustion pressure sensor.

  When the gain adjustment is performed by cutting the substrate wiring or using the laser trimmable resistor as described above, the circuit board 606 needs to be exposed to the outside, and the gain adjustment is performed in a semi-finished state where the rear housing 609 is not attached. After that, the rear housing 609 is attached and welded.

  Such a manufacturing procedure complicates the process and leads to an increase in manufacturing cost. Further, since the amplification factor is adjusted in a state different from that of the finished product, the amplification factor in the state of the finished product may be different from the amplification factor at the time of adjustment, and there is a problem that the desired amplification factor is not set correctly.

  The gain is generally adjusted while actually applying pressure to the sensor and monitoring the output. However, in the case of the above method, the cut pattern and the written trimmable resistance cannot be restored. Therefore, there is a problem that it is difficult to adjust with high accuracy.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a piezoelectric sensor capable of adjusting an amplification factor and the like with high accuracy in a short time in a finished product state. .

In order to solve the above problems, a piezoelectric sensor according to the present invention includes a piezoelectric element for detecting pressure, an integration circuit that integrates a current signal output from the piezoelectric element into a voltage signal, and Amplifying circuit for amplifying output and outputting to outside, reference voltage source for defining offset voltage of output signal outputted from said amplifying circuit, and writable memory for storing information for setting amplification factor of said amplifying circuit A housing that houses the piezoelectric element, the integrating circuit, the amplifier circuit, the reference voltage source, and the memory, one end connected to the memory housed inside the housing, and the other end is arranged so as to be exposed to the outside of the housing, the information and a write terminal for writing to the memory.
In this piezoelectric sensor, the amplifier circuit includes an amplification operational amplifier and a variable resistor, and the memory stores information on the variable resistor.
The reference voltage source includes another variable resistor for setting the offset voltage, and the memory further stores information on the other variable resistor for setting the offset voltage. Can be characterized.
The clip circuit further includes a clip circuit that is housed in the housing and limits the output of the amplifier circuit to a specified range, and the clip circuit includes another variable resistor for setting a clip voltage. The memory may further store information on the another variable resistor for setting the clip voltage.
The writing terminal may be provided on an external connection connector that connects the integrating circuit and the amplifier circuit housed in the housing to the outside of the housing. .

The piezoelectric sensor of the present invention is a piezoelectric element for detecting pressure, an integration circuit that integrates a current signal output from the piezoelectric element and converts it into a voltage signal, and amplifies the output of the integration circuit, an amplifier circuit for outputting to the outside, a reference voltage source which defines the offset voltage of an output signal output from said amplifying circuit, and writable memory for storing information for setting the offset voltage of the reference voltage source, the A housing that houses the piezoelectric element, the integrating circuit, the amplifier circuit, the reference voltage source, and the memory inside, and one end connected to the memory housed inside the housing, and the other end It is arranged so as to be exposed to the outside of the housing, the information and a write terminal for writing to the memory.
In this piezoelectric sensor, the reference voltage source may define the offset voltage using a variable resistor, and the memory may store information on the variable resistor .

The piezoelectric sensor of the present invention is a piezoelectric element for detecting pressure, an integration circuit that integrates a current signal output from the piezoelectric element and converts it into a voltage signal, and amplifies the output of the integration circuit, An amplifier circuit that outputs to the outside, a reference voltage source that defines an offset voltage of the output signal output from the amplifier circuit, a clip circuit for limiting the output of the amplifier circuit to a specified range, and a clip of the clip circuit A writable memory for storing information for setting a voltage ; a housing for housing the piezoelectric element, the integrating circuit, the amplifier circuit, the reference voltage source, the clip circuit, and the memory; and one end of the housing is connected to the memory housed within the body, the other end is arranged so as to be exposed to the outside of the housing, the writing end for writing the information in the memory It is equipped with a door.
In this piezoelectric sensor, the clip circuit defines the clip voltage using a variable resistor, and the memory stores information on the variable resistor .

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the piezoelectric sensor which can adjust an amplification factor with high precision in a short time in a product completion state.

The figure which shows one Example of the piezoelectric sensor of this invention (Example 1) The figure which shows the structural example which changes resistance value with the memory contents The figure which shows the structural example of the conventional combustion pressure sensor The figure which shows the example of the resistance for the conventional gain adjustment The figure which shows the other structural example of the conventional combustion pressure sensor Exploded perspective view showing an example of the mechanical structure of a combustion pressure sensor (A), (b) is a figure which shows the connection terminal part of the piezoelectric sensor of this invention, and the exterior. Diagram showing a configuration example when the write terminal is also used as a user terminal The figure which shows one Example of the piezoelectric sensor of this invention (Example 2) The figure which shows the structural example which makes the reference voltage variable (A), (b) is a figure for demonstrating the combustion pressure sensor with a clip function. The figure which shows one Example of the piezoelectric sensor of this invention (Example 3)

  A specific embodiment of the piezoelectric sensor of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing an embodiment of the present invention. The same configuration as that of the conventional example shown in FIG. In FIG. 1, 101 is a piezoelectric element, 102 is a DC blocking capacity, 103 is a discharge resistance, 104 is a charging capacity, 105 is an operational amplifier for integration, 112 is a feedback terminal, 113 is a signal output terminal, 115 Is a signal input terminal, 106 is a reference voltage source, 107 is an amplification resistor a, 108 is an amplification resistor b, 109 is an operational amplifier for amplification, 110 is an integrated circuit, and 111 is a nonvolatile memory. Yes.

  The piezoelectric element 101 has a pair of electrodes on its surface, and outputs a charge signal from the electrodes in accordance with the stress applied to the piezoelectric element 101. The piezoelectric element 101 has one electrode grounded, and the other electrode connected to the negative input terminal of the integration operational amplifier 105 via the DC blocking capacitor 102.

  The integration operational amplifier 105 includes a charge capacitor 104 and a discharge resistor 103 connected in parallel between a negative input terminal and an output terminal, and a reference voltage source 106 connected to the positive input terminal. An integrating circuit is configured by 105, the charging capacity 104, and the discharging resistor 103.

  The AC charge signal output from the piezoelectric element 101 is accumulated in the charging capacitor 104 provided between the input and output of the integration operational amplifier 105 via the DC blocking capacitor 102 for cutting the DC component, and is integrated. It is converted into the signal Vo1.

  The reference voltage source 106 is for applying a predetermined bias voltage to the integrating circuit and the amplifying circuit.

  An amplifier circuit that amplifies the output signal Vo1 of the integration operational amplifier 105 and outputs an output signal Vout as a piezoelectric sensor is provided at the subsequent stage of the integration operational amplifier 105. The amplifier circuit includes an amplification operational amplifier 109, an amplification resistor a107, and an amplification resistor b108. The amplification resistor b108 is connected between the negative input terminal and the output terminal of the amplification operational amplifier 109, and the positive input terminal. In this configuration, a reference voltage source 106 is connected via an amplification resistor a107.

  In this embodiment, an integration operational amplifier 105, an amplification operational amplifier 109, a reference voltage source 106, an amplification resistor a107, and an amplification resistor b108 are integrated to form an integrated circuit 110. In addition, the integrated circuit 110 includes a nonvolatile memory 111 that stores information for setting the amplification factor of the amplifier circuit. An input / output terminal is provided at a connection point between the integrated circuit 110 and the outside. A connection point between the integration operational amplifier 105 and the piezoelectric element 101 is a signal input terminal 115, an output of the integration operational amplifier 105, a discharge resistor 103, and a charge. A connection point with the capacitor 104 includes a feedback terminal 112, a connection point between the output of the amplification operational amplifier 109 and the outside includes a signal output terminal 113, and a write terminal 114 for writing information to the nonvolatile memory 111 from the outside. .

  A feature of the present embodiment is that the integrated circuit 110 includes a nonvolatile memory 111 that stores information for setting the amplification factor of the amplifier circuit. Information is input to the nonvolatile memory 111 from the write terminal 114, and the amplification resistance is determined based on the information. The value of a107 is controlled, and the amplification factor of the detection signal can be varied. The amplification resistor a107 is configured by a ladder resistor so that its value can be varied. By incorporating the nonvolatile memory 111 in the integrated circuit 110, the mounting area of the circuit block can be kept compact.

  In this embodiment, the resistor whose value is controlled by the nonvolatile memory 111 is the amplification resistor a107, but the value of the amplification resistor b108 may be controlled, or both the amplification resistor a107 and the amplification resistor b108 are controlled. It is good also as a structure.

  Information to be stored in the nonvolatile memory 111 is written by inputting serial data from a write terminal 114 connected to the nonvolatile memory 111. There are many types of serial data writing formats that are already widely used, and any of these may be selected and adopted as appropriate. Although the number of write terminals 114 varies depending on the type of format, in general, a write format having a larger number of terminals can be written at a higher speed.

  A configuration example in which the resistance value is changed by the nonvolatile memory 111 is shown in FIG. Information written from the write terminal 114 is decoded by the address / data control circuit 202 and written to the target memory cell 203. Then, according to the output level of the memory cell 203, the semiconductor switch 204 is opened and closed, and the amplification resistor a107 changes to a desired resistance value.

  The nonvolatile memory 111 includes a rewritable memory such as an EEPROM and a flash ROM, and a once-write memory such as an OTPROM and a fuse ROM. Both types can be used in the present invention.

  When a once-write memory is used, the gain can be accurately adjusted by combining a rewritable volatile memory and a nonvolatile memory. That is, in the amplification factor adjustment step, the output voltage is monitored and adjusted while writing information to the volatile memory, and when an appropriate amplification factor is determined, the value is written to the nonvolatile memory.

  Since the volatile memory has a data writing speed much faster than that of the nonvolatile memory, the configuration in which the volatile memory and the nonvolatile memory are combined is useful even when a rewritable nonvolatile memory is used.

  FIG. 7 is a view showing a connection terminal portion between the piezoelectric sensor of the present invention and the outside, and is an example in which a connection terminal portion is provided at the end of the combustion pressure sensor shown in FIG. 6 on the rear housing 609 side. As shown in FIG. 7A, the external connection connector 702 provided with a user terminal 703 (generally, in many cases, the supply power supply, the supply GND, and the output signal are provided) as the connection terminal portion of the sensor. It has. By providing the external connection connector 702 together with the write terminal 114, the gain data can be written in the sensor completed state.

  That is, in the amplification factor adjustment process at the time of manufacture, the output signal when pressure is applied to the sensor by coupling the female connector with the external connection connector 702 in which all the user terminals 703 and the write terminals 114 are electrically connected. Is monitored from the user terminal 703, data is written to the write terminal 114, and the gain is adjusted.

  The write terminal 114 is used only in the manufacturing gain adjustment process, but in the case of the connector of FIG. 7A, the non-conductive coupling corresponding to the write terminal 114 is also applied to the female socket used by the user. A hole is required. For this reason, there is a problem that the number of terminals of the user female socket increases and the cost increases.

  The structure of the connector shown in FIG. 7B solves the above problem. The write terminal 114 is provided at a position deeper than the end of the user terminal 703, and the user can use a three-terminal female connector coupled to only the user terminal 703 as it is. The female connector used in the manufacturing amplification factor adjustment step is provided with a longer coupling hole for user terminal coupling, which can be conductively coupled to the writing terminal 114, and is electrically connected to the writing terminal 114. Adjustments can be made.

  In the above description, the case where the sensor side is a male connector has been described, but the same applies to the case where the sensor side is a female connector. Further, in FIGS. 7A and 7B, only one write terminal is provided, but the present invention can be similarly applied even when there are a plurality of write terminals.

  As another method for solving the problem of the number of terminals, there is a configuration in which a dedicated write terminal is unnecessary by using both the write terminal and the user terminal. An example of the configuration of an integrated circuit corresponding to this method is shown in FIG. FIG. 8 is a diagram showing another example of the latter stage of the amplifier circuit of the present embodiment, and the former stage of the amplifier circuit has the same configuration as the piezoelectric sensor shown in FIG. The output of the amplification operational amplifier 109 and the nonvolatile memory 111 are switchably connected to the subsequent stage of the amplification circuit composed of the amplification operational amplifier 109, the amplification resistor a107, and the amplification resistor b108, and are connected to the shared terminal 813. An electronic switch 818 is provided. Further, the integrated circuit 110 is provided with a power supply monitor circuit 816 that is constantly supplied with a power supply voltage Vdd from the outside via a power supply terminal 815 and is connected to the constant power supply voltage Vdd. The power supply monitor circuit 816 constantly monitors the power supply voltage Vdd, and when the power supply voltage Vdd is less than the specified value, the electronic switch 818 is switched in a direction to connect the output of the amplification operational amplifier 109 and the shared terminal 813. On the contrary, when the power supply voltage Vdd is equal to or higher than the specified value, the electronic switch 818 is switched in the direction in which the write terminal and the shared terminal 813 of the nonvolatile memory 111 are connected.

  By setting the specified voltage higher than the power supply voltage range used by the user (for example, when the user power supply voltage is 4.5 V to 5.5 V, the specified voltage is set to 6.0 V), the user can The shared terminal 813 can always be used as an output terminal. In the manufacturing gain adjustment step, first, the power supply voltage Vdd is raised to a specified value or more, information is written to the nonvolatile memory 111, and then the power supply voltage Vdd is lowered to a user power supply voltage less than the specified value. The gain can be adjusted by the procedure of monitoring the value of Vout.

  In the above description, the case of one write terminal is described. However, the present invention can be similarly applied to the case of two write terminals by using the power supply terminal itself as a shared terminal.

  Next, another embodiment of the piezoelectric sensor of the present invention will be described. FIG. 9 is a diagram showing another embodiment of the piezoelectric sensor of the present invention. Hereinafter, description of parts common to the first embodiment shown in FIG. 1 will be omitted, and a characteristic configuration of the present embodiment will be described. In addition, the same reference numerals are used for the components common to the first embodiment shown in FIG.

  In this embodiment, the integrated circuit 110 is connected to the amplification resistor a107 and the reference voltage source 906 and stores information for determining the amplification factor of the amplifier circuit and information for determining the offset voltage of the reference voltage source 906. 911, and at least one of the value of the amplification resistor a107 and the offset voltage of the reference voltage source 906 is controlled by information written in the nonvolatile memory 911, and the amplification factor of the detection signal can be varied.

  The reference voltage VR output from the reference voltage source 906 defines the DC offset voltage of the output signal Vout. Normally, the reference voltage VR is constant. However, as shown in FIG. 9, by making the value of the reference voltage VR variable according to the contents of the nonvolatile memory 911, a combustion pressure sensor with higher added value can be obtained. Can be provided.

  One purpose of making the reference voltage VR variable is when the DC offset voltage required varies depending on the user or the model. When the offset voltage value is known in advance, an integrated circuit corresponding to the offset voltage value can be prepared, or the reference voltage value can be adjusted with a variable resistor. However, a nonvolatile memory built in the integrated circuit 110 can be used. If the offset voltage value can be adjusted according to 911, the same integrated circuit can be used for different models, and there is no need for manual variable resistance adjustment.

  Another object of making the reference voltage VR variable is fine adjustment of the reference voltage. In general, the reference voltage source is often composed of a band gap regulator that is not easily affected by variations in semiconductor manufacturing. .

  When such a variation in offset voltage cannot be allowed on the user side, it is necessary to finely adjust the reference voltage to suppress the variation. When no pressure signal is input, a DC offset voltage is output as the output signal Vout. Therefore, the reference voltage can be finely adjusted by writing data to the nonvolatile memory 911 while monitoring the output signal Vout. it can.

  An example of a circuit configuration for changing the reference voltage is shown in FIG. The reference voltage source 906 includes a band gap regulator 1001, an operational amplifier 1002, and two variable resistors 1003 and 1004. The output of the bandgap regulator 1001 is connected to the GND potential via the positive input terminal of the operational amplifier 1002 and the variable resistor 1003, and the variable resistor 1004 is connected between the negative input terminal and the output terminal of the operational amplifier 1002. Has been. The variable resistors 1003 and 1004 are connected to the nonvolatile memory 911.

  The voltage VB output from the band gap regulator 1001 is converted into a reference voltage VR by the operational amplifier 1002 and the two variable resistors 1003 and 1004. By controlling the resistance values of the variable resistors 1003 and 1004 with a signal from the nonvolatile memory 911, the value of the reference voltage VR can be adjusted.

  In the above-described two purposes of changing the DC offset voltage, the change for each model, and the fine adjustment, the adjustment accuracy and the adjustment range are greatly different. For this reason, in order to be able to perform both adjustments, it is better to prepare two sets of variable resistors so that coarse adjustment and fine adjustment can be controlled separately.

  An automotive engine combustion pressure sensor as a piezoelectric sensor may require an output voltage clipping function. This is a function that makes voltage clipping control work for voltages that exceed the predetermined upper and lower limit voltages, so that the sensor always outputs a voltage within the range from the lower limit to the upper limit. Used for diagnosis. If the voltage outside the clip voltage range is monitored by the engine-side ECU that receives the sensor output, an abnormal situation such as sensor failure or cable disconnection is assumed.

  FIG. 11 is a diagram for explaining a combustion pressure sensor having a clip function, wherein (a) is a graph showing an example of an output voltage of the combustion pressure sensor having a clip function, and (b) is a voltage clip. It is a figure which shows the example of a circuit. In FIG. 11A, the solid line indicates the output voltage, and when the waveform exceeds the clip upper limit voltage, the voltage is clipped to the upper limit voltage and output.

  FIG. 11B is a circuit diagram showing an example of a voltage clipping circuit using bipolar transistors. The upper stage in the figure is the upper limit clipping circuit and the lower stage is the lower limit clipping circuit with respect to the output of the amplifier circuit.

  In the upper limit clipping circuit, the gate of the npn transistor is connected to the connection point of resistors 1105 and 1106 connected in series between a power supply voltage Vdd (not shown) and GND, the collector of the npn transistor is connected to the power supply voltage Vdd, and the emitter is connected to the resistor. And is connected to GND. The emitter of the npn transistor is connected to the base of the pnp transistor. The collector of the pnp transistor is connected to GND, and the emitter is connected to the amplifier circuit output line. The voltage obtained by subtracting the base-emitter voltage of the npn transistor from the divided voltage of the resistors 1105 and 1106 and adding the base-emitter voltage of the pnp transistor is the maximum specified voltage.

  In the lower clip circuit, the gate of a pnp transistor is connected to the connection point of resistors 1107 and 1108 connected in series between a power supply voltage Vdd (not shown) and GND, the collector of the pnp transistor is connected to GND, and the emitter is connected to a resistor. And is connected to the power supply voltage Vdd. The emitter of the pnp transistor is connected to the base of the npn transistor. The collector of the npn transistor is connected to the power supply voltage Vdd, and the emitter is connected to the amplifier circuit output line. The divided voltages of the resistors 1107 and 1108 are substantially equal to the minimum specified voltage.

  Normally, the clipping voltage is constant, but like the offset voltage described in the second embodiment, by making it variable according to the contents of the nonvolatile memory, a combustion pressure sensor with higher added value can be provided. . FIG. 12 shows a configuration example.

  Similar to the offset voltage described in the second embodiment, the purpose of making the clip voltage variable is to cover the difference in setting depending on the model and to cope with fine adjustment. In the case of the clip circuit shown in FIG. 11B, the clip voltage can be changed by changing the values of the resistors 1105, 1006, 1107, and 1108. FIG. 12 is a diagram showing another embodiment of the piezoelectric sensor of the present invention. Hereinafter, description of the parts common to the first and second embodiments shown in FIGS. 1 and 9 will be omitted, and the characteristic configuration of the present embodiment will be described. In addition, the same reference numerals are used for the components common to the first embodiment shown in FIG. In this embodiment, a clip circuit 1215 and a nonvolatile memory 1211 are provided in the integrated circuit 110 and subsequent to the amplifier circuit. The nonvolatile memory 1211 is connected to the amplification resistor a107, the reference voltage source 906, and the clip circuit 1215, and information for determining the amplification factor of the amplifier circuit, information for determining the offset voltage of the reference voltage source 906, and clipping of the clip circuit 1215 Information for determining the voltage is stored, and at least one of the value of the amplifying resistor a107, the offset voltage of the reference voltage source 906, or the clip voltage of the clip circuit 1215 is controlled and detected by the information written in the nonvolatile memory 1211 The signal amplification factor can be varied. In order to control the clip voltage of the clip circuit 1215, the clip circuit 1215 is stored in the nonvolatile memory 1211 with any one of the resistors 1105, 1106, 1107, and 1108 in the voltage clip circuit shown in FIG. The resistance value in the clip circuit 1215 may be changed according to the information.

  Although the present invention has been described based on the three embodiments, the piezoelectric sensor of the present invention is not limited to this embodiment, and various modifications can be made to the above-described embodiments without departing from the spirit of the present invention. Including those with.

101, 301, 501: Piezoelectric element, 102, 302: DC blocking capacity, 103, 303, 503: Discharge resistance, 104, 304, 504 ... Charging capacity, 105, 305, 505 ... Operational amplifier for integration, 106, 306, 506, 906: Reference voltage source, 107, 307, 507 ... Amplification resistors a, 108, 308, 508 ... Amplification resistors b, 109, 309, 509 ... Amplification operational amplifiers, 110, 310 ... Integrated circuits, 111, 911, 1211: Non-volatile memory, 112, 312 ... Feedback terminal, 113, 313 ... Signal output terminal, 114 ... Write terminal, 115, 315 ... Signal input terminal, 202 ... Address / data control circuit, 203 ... Memory cell, 204 ... Semiconductor Switch, 601 ... Diaphragm head, 602 ... Fixing screw, 603 ... Front housing 604 ... Piezoelectric element, 605 ... Conductor, 606 ... Circuit board, 607 ... Circuit case, 609 ... Rear housing, 702 ... Connector for external connection, 703 ... User terminal, 813 ... Dual terminal, 815 ... Power supply terminal, 816 ... Power supply monitor Circuit, 818 ... Electronic switch, 1001 ... Band gap regulator, 1002 ... Operational amplifier, 1003, 1004 ... Variable resistance, 1105, 1106, 1107, 1108 ... Resistance, 1215 ... Clip circuit

Claims (9)

A piezoelectric element for detecting pressure;
An integration circuit that integrates the current signal output from the piezoelectric element and converts it into a voltage signal;
An amplifying circuit for amplifying the output of the integrating circuit and outputting to the outside;
A reference voltage source defining an offset voltage of the output signal output from the amplifier circuit;
A writable memory for storing information for setting the amplification factor of the amplifier circuit;
A housing housing the piezoelectric element, the integrating circuit, the amplifier circuit, the reference voltage source and the memory;
With one end connected to said memory internally housed in the housing, the other end is arranged so as to be exposed to the outside of the housing, Ru and a write terminal for writing the information in the memory Piezoelectric sensor. The amplifier circuit has an operational amplifier for amplification and a variable resistor,
The memory stores information on the variable resistor.
The piezoelectric sensor according to claim 1. The reference voltage source has another variable resistor for setting the offset voltage,
The memory further stores information of the other variable resistor for setting the offset voltage.
The piezoelectric sensor according to claim 2. A clip circuit that is housed inside the housing and limits the output of the amplifier circuit to a specified range;
The clip circuit has another variable resistor for setting a clip voltage,
The memory further stores information of the another variable resistor for setting the clip voltage.
The piezoelectric sensor according to any one of claims 1 to 3. The write terminal, according to claim 1 to 4, characterized in that provided on the connector for external connection which connects the outside of said housing said integration circuit and said amplifier circuit and the casing is accommodated in the The piezoelectric sensor according to any one of the above. A piezoelectric element for detecting pressure;
An integration circuit that integrates the current signal output from the piezoelectric element and converts it into a voltage signal;
An amplifying circuit for amplifying the output of the integrating circuit and outputting to the outside;
A reference voltage source defining an offset voltage of the output signal output from the amplifier circuit;
A writable memory for storing information for setting the offset voltage of the reference voltage source;
A housing housing the piezoelectric element, the integrating circuit, the amplifier circuit, the reference voltage source and the memory;
With one end connected to said memory internally housed in the housing, the other end is arranged so as to be exposed to the outside of the housing, Ru and a write terminal for writing the information in the memory Piezoelectric sensor. The reference voltage source defines the offset voltage using a variable resistor,
The memory stores information on the variable resistor.
The piezoelectric sensor according to claim 6. A piezoelectric element for detecting pressure;
An integration circuit that integrates the current signal output from the piezoelectric element and converts it into a voltage signal;
An amplifying circuit for amplifying the output of the integrating circuit and outputting to the outside;
A reference voltage source defining an offset voltage of the output signal output from the amplifier circuit;
A clip circuit for limiting the output of the amplifier circuit to a specified range;
A writable memory for storing information for setting a clip voltage of the clip circuit;
A housing housing the piezoelectric element, the integrating circuit, the amplifier circuit, the reference voltage source, the clip circuit, and the memory;
With one end connected to said memory internally housed in the housing, the other end is arranged so as to be exposed to the outside of the housing, Ru and a write terminal for writing the information in the memory Piezoelectric sensor. The clip circuit defines the clip voltage using a variable resistor,
The memory stores information on the variable resistor.
The piezoelectric sensor according to claim 8.

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